The proliferation of digital multimedia, along with the ever-increasing bandwidth in internet communications, has made the management of digital copyright more and more challenging. Since any end user receiving a copy of multimedia content can redistribute the copy to other users, a mechanism to trace the illegal distributor needs to be established to protect the digital copyright. Multimedia fingerprinting is a way to embed unique IDs into each user's multimedia content. Because the embedded fingerprint is uniquely associated with the user to whom the copy was given, extraction of that fingerprint in a pirated copy uniquely identifies the user associated with the fingerprint.
Since multimedia data can be slightly modified without causing perceptual distortion, a fingerprint may be embedded within the data without degrading the end user's experience. There have been a number of prior works on fingerprinting image and audio signal. However, the research into video fingerprinting has been quite limited. Usually, as the host signal for fingerprinting changes, the fingerprinting scheme also needs to be adapted. For example, in a color image of natural scenes, the space for fingerprint embedding is usually much larger than in a binary image. Naturally, we would expect more embedding capacity from video. However, the large volume of data in video introduces both favorable and unfavorable aspects. A favorable aspect is that the embedding capacity of video is much higher than still images, and therefore the robustness of fingerprinting is increased. An unfavorable aspect is that the spatial and temporal redundancy of video signals may be exploited by attackers. Therefore, the design and engineering of video fingerprinting schemes is more sophisticated than fingerprinting still images and audio.
While the fingerprint designer's effort to protect digital copyright, the attackers also have strong incentive to remove the fingerprint. For example, popular marketing schemes send popular motion pictures to theaters prior to a period of time during which they are sold “on video,” e.g. on a DVD medium. If a pirate can sell the movie on DVD during its theater run, a huge profit can be realized. In attacking a fingerprinting scheme, the attackers' goal is to fool the fingerprint detector so that it will not be able to detect or correctly identify a finger print. For attackers, time complexity and perceptual quality are also important considerations, since the value of multimedia lies in part in its timeliness and perceptual quality. Accordingly, a group of attackers, each in possession of a fingerprinted copy of a video may conspire to form a collusion attack. Such an attack attempts to attenuate or remove the fingerprint embedded in each copy. When the number of fingerprinted copies within the collusion attack is large enough, e.g. 30 to 40 colluders, the utility of the fingerprint is reduced so much that it may not be possible for the fingerprint detector to detect the existence of fingerprint in the colluded copy.